A Unity Power Factor Active Rectifier and DC Bus Control system is described in this
thesis.
The aim of an active rectifier controller is to draw sinusoidal input current with unity
power factor, and to provide fast response to DC load disturbance, whilst maintaining
the DC link voltage as constant as possible. To achieve this aim, a current control
structure based on voltage vector modulation has been developed using both stationary
and synchronous reference frames. To improve response speed and stability, reduce
transient overshoot, and overcome the drawback caused by the inherent dead time delay
in the digital control loop, a Smith Predictor is introduced into the control loop to
compensate for the dead time delay. To speed up the response to DC link current
disturbance, the control structure incorporates DC bus voltage feedback regulation plus
DC link feed-forward current control. For mains supply synchronization, a software
digital Phase Locked Loop (PLL) is used, designed for low sensitivity to supply voltage
noise. To further improve performance, a double update pulse width modulation (PWM)
mode is utilised.
To implement feed-forward current control without the need for multiple DC link current
sensors and associated communication channels in applications where the common DC
bus system feeds multiple variable speed drives, a robust minimum order DC link current
observer has been designed to provide the required feed-forward current signal.
To investigate the performance of the active rectifier controller, a simulation program
based on VissimTM has been developed and simulations carried out for both 20A and
500A step change load currents. An experimental system has been built using a
ADMC401 digital signal processor as the control core, and experiments conducted using
different control schemes. Both simulation and experimental results show the validity of
the control model